Phaedrus Audio PHILTER User manual

Ver. 0.1 - ©Phædrus Audio Ltd. 2011 All rights reserved.
User Manual for
PHILTER - passive EQ and tube amplifier
This manual is also available as a pdf do nload, Go to: .phaedrus-audio.com

Ver. 0.1 - ©Phædrus Audio Ltd. 2011 All rights reserved.
Preface – About Phædrus Audio
Phædrus Audio as formed to design, manufacture and sell high-quality products for the
professional and semi-professional audi o market. Phædrus Audio's founders remain inspired by the
music and the recording practices of the fifties and sixties, and are moti vated to re-establish the
values of the great audio-technology legends of the past ith their i deals of transparency, hand-
built quality, and serviceabili ty. Using modern manufacturi ng techniques and the benefits of
modern component technology, Phædrus Audio's aim is to reproduce the quality and character of
classic equipment but in a modern, highly reliable, and cost-effecti ve ay.
Chapter 1 - Background
The Phædrus Audi o products came about because t o, recording musicians anted to o n a
"classic" console from the nineteen-sixties. Ideally a famous EMI, REDD, all valve (vacuum tube)
mixer used to record The Beatles.
But those desks make a collection of
hen's teeth look positi vely prosaic -
as ell as cheap! So, e set about
researching ith the idea of
producing a replica console.
In order to do this, fi rst i t as
necessary to have a design for the
amplifi er modules around hich the
mixers of this vintage are organised.
In the famous EMI REDD mi xers,
these amplifiers ere either the
German manufactured V72(S)
amplifi ers or the, very rare, EMI
built, REDD.47 ampli fiers.

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V72 and REDD.47 modular amplifiers
Ironically, despite the fact that many more V72 amplifiers exist than do REDD.47s, the EF804
valves hich the German amplifiers use are no longer in current production and are becomi ng very
expensive: hereas the EF86 and ECC88 (E88CC) valves employed in the REDD ampli fiers remain in
production and are idely available. So, a ne ampli fier, designed from the common source of
Mullard's reference audi o designs, and thereby sharing a common heritage i th the REDD
amplifi ers, as developed. We called this amplifier the Phaedrus "PHILHARMONIC" (li terally ,
music lovi ng
). This PHILHARMONIC amplifier forms the heart of the Phædrus Audio LONDON
Mark II console. The PHILHARMONIC amplifier circuit is descri bed in detail belo in section
Circuit descripti ons .
Mullard published many reference designs which were used by EMI in developing the REDD
amplifiers. At Phædrus Audio, we went back to these same references to develop our products.
The prototype London Console (Mark II)

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Construction - or star earths (grounds) and curly tracks
Given their vintage, the V72 amplifiers and the REDD.47 amplifi ers ere built on a metal chassi s,
ith the components hard ired onto tag-strips. Although Phædrus Audio equipment uses printed
circuit boards to ensure consistent performance and r eli abi lity, the equipment follo s "classic"
practices such as star earths and "natural contour" tracking, just like hook-up ire.
Every Phædrus Audio product i s hand assem bled and individually tested. A test pro-forma is
provided ith every unit. Phædrus Audi o offer comprehensive service for products both inside and
outside of their arranty peri od.

Ver. 0.1 - ©Phædrus Audio Ltd. 2011 All rights reserved.
Chapter 2 - Warranty and Service
Please register your purchase ith Phaedrus Audi o at .phaedrus-audio/registration.htm . This
ill si mplify service & repair should you need thi s service. Your name ill be placed on our mailing
list (unless other ise requested) for future updates and ne product announcements.
Service
If you experience a problem ith a Phædrus Audio Ltd. product, contact:
[e-mail]
TELEPHONE: [phone]
Skype ID: phaedrusaudio
We ill diagnose the problem remotely and advise you of the arranty status. If a repair or
replacement is required, e ill issue a Return Merchandise Authorization (RMA) number and tell
you here to send the unit to be repaired. You MUST have an RMA number before you return the
equipment to Phædrus Audi o Ltd.'s support service. Be sure to ri te RMA number on outside of
shipping box and to include your name, address, phone number, a copy of original sales i nvoice and a
detailed descri ption of the problem. Phædrus Audio Ltd. ill not accept responsibili ty for loss or
damage in shi pping or for equipment returned ithout vali d paper ork and/or a valid RMA number.
Remember, arranty is void if product serial numbers have been removed or altered, or if the
product has been damaged by abuse, accident or unauthorized modification and/or repair (see
Phædrus Audio Ltd. Limited Warranty for details). There are no user serviceable parts inside.
PLEASE RETAIN YOUR SALES RECEIPT. IT IS YOUR PROOF OF PURCHASE COVERING YOUR
LIMITED WARRANTY. LIMITED WARRANTY IS VOID WITHOUT SUCH PROOF OF
PURCHASE.
Phædrus Audio Ltd.'s Limited Warranty
This limit ed arranty is valid only if you purchased the product from Phædrus Audio Ltd. of from a Phædrus Audio
authorized dealer in the country of purchase: a list of authorized dealers can be found on Phædrus Audio ebsite
.phaedrus-audio.com, or by contacting [e-mail]. Phædrus Audio Ltd. arrants that the equipment it
manufactures shall be free from defects in material and orkmanship for a period of one (1) year from the original date of
purchase; unless a longer minimum arranty period is mandated by applicable local la s. If equipment fails due to such
defects ithin this period, Phædrus Audio ill, at its option, repair or provide a replacement for the defective part or
product. Valves (va cuum tub es) are excluded from the one-year arranty, but are arranted for 90 days from day of
purchase. This arranty does not extend to any Phædrus Audio Ltd. product that has been damaged or rendered defective
as a result of: accident, misuse, or abuse; or by the use of parts not manufactured or supplied by Phædrus Audio Ltd.; or by
unauthorized modification or attempted repair to the product; or by acts of God/Nature ( accident, fire, flood, etc) or any
other condition that is beyond the control of Phædrus Audio Ltd. Ther e are no user s erviceable parts ins ide. This limited
arranty is invalid if the factory-applied s erial number has been a ltered or removed from the product. This limit ed
arranty is extended exclusively to the or iginal buyer (customer of Phædrus Audio Ltd., or authorized retail dealer) and is
not transferable to anyone ho may subsequently purchase the product. No other person (retail dealer, etc.) shall be
entitled to give any arranty promise on b ehalf of Phædrus Audio Ltd. Phædrus Audio Ltd. makes no other arranties,
expressed or implied, of merchantability, fitness for a particular purpose or other ise. Phædrus Audio Ltd. liability is
limited to repair or replacement by Phædrus Audio Ltd., at its sole discretion and, in no event, ill Phædrus Audio Ltd. be
liable for any direct, indirect, special, incremental or consequential damages resulting from any defect in the product,
including lost profits, damage to property and, to the extent permitted by la , damage for personal injury, even if Phædrus
Audio Ltd. has been advised of the possibilities of such damages.

Ver. 0.1 - ©Phædrus Audio Ltd. 2011 All rights reserved.
Shipping Charges
For any hard are defects experienced by the customer hile the product is under arranty, Phædrus Audio Ltd. ill incur
the shipping cost to the customer and the customer is responsible for the shipping costs to Phædrus Audio Ltd's
designated after-sales service office. For defective products that are out of arranty the customer is responsible for all
shipping costs to and from Phædrus Audio Ltd’s designated after-sales service office.
Extended warranty and out-of-warranty services
Various services are available from Phædrus Audio Ltd. These include repair services for
equipment once the arranty period has expired, and the abi lity to extend the arranty peri od.
These are:
PHILTER-REP - Repair of a defective PHILTER equaliser, charged at a flat-rate
PHILTER-MISEAJOUR - Mise à jour for PHILTER*
PHAE-EXTWARR - Extends standard arranty (see above) by a further year**
* A mise à jour service includes a complete inspecti on, re-valve (re-tube) and the implementation
of any engineering updates as ell as a re-test to per formance specification.
** If extended arranty is ordered after the initial arranty has expired then the intervening
period is charged ithout exception.
Please contact your dealer or Phædrus Audio Ltd. for current prices.
Warranty service conditions are subject to change ithout notice. For the lat est arranty terms and conditions and
additional information r egarding Phædrus Audio Ltd. limit ed arranty, please s ee complete details online at
.phaedrus-audio.com .
Chapter 3 - Safety
General
Before using any piece of equipment manufactured by Phædrus Audio Ltd., be sure carefully to
read the applicable i tems of these operati ng instructions and the safety suggestions. Keep them
for future reference. Follo the arnings indicated on the unit, as ell as in the operating
instructions.
Selection of PSU
Suitable PSUs for the Phædrus Audio Ltd. products are available as line items from Phædrus
Audio.
They are:
PHAE-PSU(110) - 110V mains plugtop PSU: plug is North American type.
PHAE-PSU(220Euro) - 220V mains plugtop PSU; plug is European type
PHAE-PSU(220UK) - 220V mains plugtop PSU; plug is 3 pin 13 AMP, British type
A 12V AC supply is required for the Phædrus Audio PHILTER. A direct current (DC) supply is NOT
suitable and ill damage the unit. If a supply is sourced else here than from Phædrus Audio, it
must have the follo ing specifications:

Ver. 0.1 - ©Phædrus Audio Ltd. 2011 All rights reserved.
•12V AC, 12 Watt supply or greater (> or = 1000mA supply current)
•Must be suitable for connecti on to the appropriate mains voltage
•Must be Class-II, double-insulated
•Must have 30% regulation or better
•Must contain one-shot thermal fuses, resettable fuses, or Polys itches for over-current
protection.
UK and Euro units should comply ith EN 60950-1 and CE requirements and o ly PSUs with UL
a d CSA approvals should be provi ded on North American units. Units suppli ed to other countri es
should be verified to comply ith the relevant standards hich obtain in those terri tories.
User Access & Servicing
Phædrus Audio equipment employs thermionic valve (vacuum-tube)
technology and employs hazardous voltages for the hi gh-tension
suppli es. THE USER SHOULD NOT ATTEMPT TO SERVICE THE
UNIT. ALL SERVICING SHOULD BE REFERRED TO QUALIFIED
SERVICE PERSONNEL OR FACTORY ONLY.
Phædrus Audio products should NEVER be connected to the external
po er supply or in any other ay energised hen the case i s opened and/or the circuit board is
accessible.
Ground (earth) issues
Phædrus Audio Ltd.'s products are all po ered by external (12V AC) po er suppli es hich should
be double insulated, class-II types (see above). It should therefore be appreciated that,
A CONNECTION TO EITHER THE PHAB, the PHAME, PHILTER of the PHI product
CAN NEVER BE RELIED UPON PROVIDE A PROTECTIVE OR SAFETY EARTH
(GROUND). Thi s advice obtains IRRESPECTIVE OF THE SETTINGS OF ANY "EARTH
OR GROUND LIFT" SWITCHES .
General Safety Instructions
•Do not operate Phædrus Audio equipment near any source of ater or in excessively moist
environments.
•Keep your Phædrus Audio equipment a ay from babies, chi ldren and pets.
•Do not let objects do not fall, or liquids be spilled, i nto the enclosure.
•Situate the Phædrus Audio equipment a ay from heat sources or other equipment that
produce heat.
•Ensure Phædrus Audio equipment has adequate venti lation. Improper ventilati on ill cause
overheating, and can damage the equipment.
•When cleaning Phædrus Audio equipment, remove all connections to the unit; includi ng
po er and gently ipe ith a clean lint-free cloth; if necessary, gently moistened ith
luke arm or distilled ater. Use a dry lint-free cloth to remove any remaining moisture.
NEVER use aerosol sprays, solvents, or abrasives on Phædrus Audio equipment.
•Phædrus Audio equipment should be serviced by qualified service personnel or returned to
Phædrus Audio Ltd. hen: an object (or objects) have fallen into the enclosure; or liquid
has fallen into, or been spilled into the unit; or the unit has been exposed to rain or high

Ver. 0.1 - ©Phædrus Audio Ltd. 2011 All rights reserved.
humidity; or the unit does not operate normally or exhibits a marked change in
performance; or the unit has been dropped, or the enclosure has been damaged.
Chapter 4 - About Valves (Vacuum Tubes)
Valve (tube) types
The Phædrus Audi o PHAB and PHAME preamplifiers and
the PHILTER equaliser employ an EF86 pentode input
valve (tube) and an ECC88, or E88CC, valve (tube) as the
output devi ce. Positi ons for the valves are very clearly
marked on the PCB silkscreen as indicated in the
illustration. The valves (tubes) that are installed in
Phædrus Audio’s products duri ng assembly are selected
to give the best possible per formance. We offer versions of all products ith NOS (rather than
current production) valves. But these must be chosen carefully, and be pr e-screened. Replacing the
suppli ed valves (tubes) ith different, collectible, or “high-end” valves (tubes) types may not
affect any improvement and mi ght cause deterioration of performance.
EF86
The EF86 is a lo noise pentode, ori ginally manufactured by many di fferent factori es and
branded by Phili ps, Mullard, Telefunken, Valvo, and GEC, TESLA and Siemens/RFT. Many
NOS valves are still available. Equivalents include the CV2901 (the UK service desi gnati on
for the EF86) and the CV4085; a special quality versi on for mi litary use. The EF86 tube is
sti ll being produced in Russia and in the Slovak Republi c under JJ Electronics brand name
(formerly Tesla). Chi nese close equivalents are also still being manufactured.
ECC88
The ECC88 is a frame-gri d, sharp cut-off, t in (dual) triode ith an internal,
separating screen. The valve as originally designed for servi ce in the front ends of
VHF radio recei vers. The ECC88 (E88CC) tube type is equivalent to the North
American 6DJ8 tubes and the (rare) military branded CV2492. The transposition of
the fi gures from ECC88 to E88CC as Mullard's ay of denoting a special quali ty
build and is equivalent to the US 6922. Russi an 6N1P tubes and the Chinese 6N1
tube are NOT equivalent. NEVER i stall a 6N1(P) i the Phædrus Audio PHAB,
PHILTER or PHAME product. The ECC88 valve is si ll being manufactured in Chi na
and in the Slovak Republic under JJ Electronics brand name (formerly Tesla).
12AU7 or ECC82
The 12AU7 is a popular, miniature 9-pin medium-gain dual triode valve (tube)
and is used in many instrument and hi-fi amplifiers. Both triodes are used, in
cascade, in the Phædrus Audio PHI product. The 12AU7 is also kno n in
Europe under its Mullard-Phi lips tube designation ECC82. Thi s tube is idely
available both ne and NOS and a number of special quality equivalents are
available. Current producti on of 12AU7 takes place in Russia, Slovakia, and

Ver. 0.1 - ©Phædrus Audio Ltd. 2011 All rights reserved.
China. Phædrus Audio selects and recommends the long anode (plate) version of the ECC82
(ECC802S) or 12AU7 valve for application in the PHI DI-Box.
Valve (tube) lifetime
You should replace the valves in the tubes in the Phædrus Audio products only hen you start to
notice changes in the sound quali ty. If the gain of the preamplifier decreases noticeably, then this
is certainly evidence of the onset of valve (vacuum tube) failure. Before this, the tone may become
"dull" and transients may be become "blunted".
That said, the li fetime of a valve (tube) i s largely determined by the lifetime of i ts cathode
emission and the small-si gnal valves (tubes) used in the PHAB, PHAME, PHILTER and PHI use oxide
cathodes, hich can provide adequate cathode emi ssion for 100,000 hours or more. That's over
eleven year’s continuous use. So do not replace valves (tubes) just because they have seen a fe
years service.
Phædrus Audio Ltd. can provide suitabl e valves (tubes) as spares hich, after a burn-in period, are
screened for best performance in your Phædrus Audio product. These are available as line items:
PHAE-12AU7 – Selected 12AU7/ECC82 type valve
PHAE-ECC88 - Selected ECC88 type valve
PHAE-EF86 - Selected EF86 type valve
Please contact your dealer or Phædrus Audio Ltd. for current prices.
Chapter 5 - Instructions for use
Phædrus Audio’s products employ valves (vacuum tubes) as the ONLY ACTIVE DEVICES in the
audio path. Valves (vacuum tubes) and their associated circuitry need ti me to reach an el ectronic
equilibri um before they ill operate at optimal specifi cations. Please therefore allo these
products to arm up for, at least, 5 to 10 minutes before using them in your signal chain. To
prolong the life of your valves (tubes), it is recommended that you turn off these units hen not in
use.

Ver. 0.1 - ©Phædrus Audio Ltd. 2011 All rights reserved.
Typical connection set-up for the PHILTER
PHILTER
Application and connections
The PHILTER equaliser is a self-contained, line-level device. The loss due to the passive equaliser
circuitry is made-up in the included, internal line-amplifier. The figure belo is a block-diagram, of
the unit. The unit is connected by balanced, earth-free, transformer-coupled connections on
professional XLR connectors. Operating levels are covered belo .
One ord of arning: remember the line-amplifier makes up for the loss in the passive Q circuits
hen the controls are central (and no boost is applied). In a passi ve equali ser, boost is actually
provided by reversing the loss of the equaliser over a range of fr equencies. In other ords, hen
boost i s applied, bass frequencies are “un-cut”. This means that, hen large degrees of boost are
appli ed, it may be necessary to reduce the signal level sent to the PHILTER to stop it overloading.
Architecture of the PHILTER equaliser

Ver. 0.1 - ©Phædrus Audio Ltd. 2011 All rights reserved.
Controls
Bass, Treble and Frequency-select controls
The equalisation controls on the PHILTER are si mple and intuitive to operate. Remember, these
circuits ere i nvented ell before the complex, analogue equalisers of the nineteen-seventies.
When the middle frequency-control is turned to the t o most anti-clock ise positions, the bass
and treble controls (marked ith the appropriate music clefs) act as they do on a hi -fi; as a boost
and cut control: clock ise to boost (in 2dB steps); anit-clock ise to cut (i n 2dB steps). The central
control may be used to modify the character of the treble-frequency boost. Depending on the
frequency setting: 2.5kHz; 3.5kHz; 5kHz; 8kH z; 10kHz; 12kHz, hen the treble control is rotated
clock ise beyond the central position, boost is applied ith a broad peak in the response at the
indi cated frequency. Note that this control is NOT active hen treble-frequency cut i s applied;
this al ays remains as a shelving response. The graph belo illustrates the 121 separate response
curves hich result form the 121 combinations of treble and bass control hen the central s i tch
selects the 5kHz, peaking-response. Note that the cut curves do not exhi bit a complementary
notch to the boost peak.

Ver. 0.1 - ©Phædrus Audio Ltd. 2011 All rights reserved.
Operating levels
Because of the vintage of the PHILTER design,
and its ori gin i n German manufactured broadcast
television and
radio equipment,
the envisaged
operating level for
this equipment is
slightly lo er than
modern recordi ng
industry
standards. When
feeding
do nstream
equipment, the output level should be set to a nominal 0dBu (0.775V RMS). This means that if
monitori ng the output on a standard VU instrument, the input attenuator should be set so that the
output level reads around -4VU, i th occasional peaks to 0VU on programme. On a digital meter,
this is equivalent to signal peaks reading +6dB above recording industry standard +4dBu ali gnment
level. Thi s is equivalent to +10dBu (or -8dBFS on equipment aligned to EBU R64-1992 standard and
-14dBFS on equipment ali gned to SMPTE RP155 as illustrated). On a broadcast standard PPM,
peaks should be set to read 6 on the BBC scale, or +8 on the European EBU scale. Output level i s
sufficient easily to modulate semi-pro' equipment (mixers, DAT, solid-state recorders and many
sound cards) to 0dBFS.
That said, the headroom on the
PHILTER is consi derabl e, and no
noticeable distorti on is evident
hen operati ng the equipment
at standard recording industry
levels of +4dBu=0VU, or even
higher. There is thus
considerable scope for
experimentation ith over dri ving this vi ntage circuitry to
explore its character i n gradual overload. For example,
peaks may be allo ed to reach +18dB above alignment level
i thout cli ppi ng. The Phædrus Audi o PHAB and the PHAME
preamplifiers and the PHILTER equaliser may thus be used
directly to feed modern A to D conversion equipment
aligned to EBU or SMPTE standards follo i ng the
recommendations illustrated (ri ght).

Ver. 0.1 - ©Phædrus Audio Ltd. 2011 All rights reserved.
Chapter 6 - Circuit descriptions
PHILTER
The Phædrus Audi o PHAB and the PHAME preamplifi ers and the PHILTER equali ser all share
roughly the same preamplifi er circuit.
The amplifier block is a t o-stage design incorporating an EF86 lo -noise pentode i n the first
stage and a paralleled ECC88 hi gh mutual-conductance double-triode as the output stage. All the
landmark ampli fier designs fr om Mullard's application laboratories specifi ed the EF86. In fact,
Mullard described the EF86 as a lo noi se pentode intended for use as a RC coupled AF voltage
amplifi ers; parti cularly in the early stages of high gain audio amplifiers, microphone preamplifiers
and magnetic tape recorders
.
The output stage comprises a dual triode valve in hich the t o devices are i red in parallel. This
paralleling of the t o triodes has the beneficial effects of doubli ng the mutual conductance and
halving the anode resistance. The latter characteristic is particularly valuable in ensuring a lo
impedance drive to the output transformer.
The output stage directly feeds the output step-do n transformer. The output is balanced and
earth free. A modest degree of negative feedback is taken from the anode of the output valve(s)
to the cathode circuit of the input stage to stabilise gain, extend frequency-response and lo er
distorti on. This feedback resistor is selected to give different gains dependi ng on the particular
product.
Performance
At recording industry line-up (0VV=+4dBu) the
magnitude of all distorti on components on a 1kHz sine
ave input are less then -55dB belo fundamental.
Thi s, and the A- eighted noise response relati ve to
maximum output, is i llustrated belo .

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Equaliser performance
Equali ser performance is best defined graphically and that is ho it i s presented belo .
Control extremes

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Peaking responses
Mi d-position response <1dB variation

Ver. 0.1 - ©Phædrus Audio Ltd. 2011 All rights reserved.
Specifications
Electrical connections
Input:
Unbalanced: 3 pin XLR Connector Balanced: 3 pin XLR Connector
Pin 1 – Ground Pin 1 – Ground
Pin 2 – (+) Signal Pin 2 – (+) Signal
Pin 3 – Connect to Pin 1 Pin 3 – (-) Signal
Output:
Unbalanced: 3 pin XLR Connector Balanced: 3 pin XLR Connector
Pin 1 – Ground Pin 1 – Ground
Pin 2 – (+) Signal Pin 2 – (+) Signal
Pin 3 – Connect to Pin 1 Pin 3 – (-) Signal
PHILTER Specification
Circuit configuration: 3 valve (vacuum tube) design
Output: Balanced, transformer coupled
Maximum out put lev el: +18dBu @ 1kHz
Input: Balanced, transformer coupled
Maximum input level: +18dBu @ 1kHz
Gain: Nominally 0dB, maximum boost is +10dB
Frequency response: 40Hz to 15kHz, ±1dB: 15Hz to 30kHz ±3dB, control flat.
Distortion: <0.2%, 1kHz @ -4VU (0dBu), gain 40dB : <1%, 40Hz @ -4VU (0dBu), gain 40dB
Noise: <-120dB referred to input
Po er supply: 12V AC
Po er consumption: 8 Watts
Phaedrus Audio Ltd. reserves the right to alter these specifications ithout notice.

Ver. 0.1 - ©Phædrus Audio Ltd. 2011 All rights reserved.
Declaration of Conformity
The Manufacturer of the Products covered by this Declaration is
Phædrus Audio Ltd.
head office address
The directives covered by this declaration are:
89/336/EEC Electromag etic Compatibility directive
73/23/EEC Low Voltage Equipme t directive
The products covered by this declaration are:
Phædrus Audio PHAB – micropho e preamplifier; Phædrus Audio PHAME – i strume t
preamplifier; Phædrus Audio PHILTER – passive equalizer & tube recovery amplifier a d
Phædrus Audio PHI – DI-Box.
The basis on which conformity is being declared:
The manufacturer hereby declares that the products i dentifi ed above comply ith the protection
requirements of the EMC directive and i th the principal elements of the safety objectives of the
Lo Voltage Equipment di rective, and that the follo ing standards have been applied:
IEC INTERNATIONAL STANDARD 60065 - Audio, video a d similar electro ic apparatus –
Safety requireme ts
The technical documentation required to demonstrate that the products m eet the requirements of
the Lo Voltage Equipment directive has been compiled and is available for inspecti on by the
relevant enforcement authoriti es. The CE mark as first applied in 2011.
Signed: Richard Brice, Tech ical Director
Date: January 2011

Ver. 0.1 - ©Phædrus Audio Ltd. 2011 All rights reserved.
Appendix - TEST PRO-FORMA
Product: PHILTER Serial Number: ________________
Tested by: ________________ Tube complement:_____________________________
V1 volts: ___________
Volts TP1: ___________ Volts TP2: ___________
Gain set: ______dB (40dB or LOW GAIN positi on)
High ain test Pass / Fail
Distortion test: Pass / Fail
PAD test: Pass / Fail
Frequency response test: HF (-3dB) extension: Pass / Fail
Frequency response test: LF (-3dB) extension: Pass / Fail
Phantom (+48) supply test: Pass / Fail / N/A
Listening test: Pass / Fail